The preparation of oximes is generally described in U.S. Pat. No. 4,323,706 directed to production of acetaldehyde oxime as follows:
"Oximes are conventionally prepared by oximating a ketone or aldehyde with an aqueous hydroxylamine-containing solution. The oxime is then recovered from the aqueous solution . . . Many oximes are easily recovered from the aqueous oximation reaction mixture because the relatively water-insoluble oxime forms a separate phase from the aqueous phase, and may be separated by decantation or the like".
Acetaldehyde oxime is thereafter described as presenting a unique recovery problem because is relatively water - soluble and therefore cannot be phase-separated.
Another method of preparation of oximes is shown in several patents issued to McBee, (U.S. Pat. Nos. 3,141,043, 3,462,488 and 3,459,802) which employ hydroxylamines in methanol solutions to carry out the oximation reaction. The oxime may be extracted with ether and recovered.
Generally, aromatic aldoximes are prepared by the reaction of aromatic aldehydes with hydroxylamine generated from hydroxylamine salts.
The present invention relates to a new and simple method for preparation of aromatic aldoximes by reaction of the correspondinq aromatic .alpha.,.alpha.-dihalides with hydroxylamine salts and which provides high yields of the oxime product and simple recovery of a high purity product, even if relatively impure aromatic dihalides are used as a feedstock.
Benzaldehyde oxime is usually prepared from benzaldehyde, as described above in the excerpt from the '706 patent. While benzaldehyde can be prepared from hydrolysis of benzal chloride, the reaction product would be separated from the by product hydrochloric acid and purified before being converted to the oxime. In one embodiment of the present invention, benzaldehyde oxime is made directly from benzal chloride, even if crude and unpurified, thus avoiding the multiple-step process cf the art.